The move will bolster Microsoft's ability to deliver a service for enforcing compliance through archiving messages while minimizing spam and viruses, the company said. Microsoft said it would continue to support and sell the entire FrontBridge product line.

The move marks the fourth time in the past year and a half that Microsoft has acquired a secondary player to increase its position in the market.

In February, it purchased Sybari Software, a provider of anti-virus, anti-spam and content-filtering technologies for enterprise customers.

In December of 2004, it purchased Giant Software, which makes anti-spyware software. In June of 2003 it purchased Bucharest, Romania-based GeCAD, which makes software for anti-virus detection and data security.

"Our commitment to listening and responding to customers really drove the union with FrontBridge, because both companies are focused on solving the same difficult messaging challenge -- ensuring customers' e-mail is compliant, better protected from spam and virus threats, and always available, even in the case of unforeseeable disaster," Dave Thompson, corporate vice president of the Exchange Server Group at Microsoft, said in a statement.

Microsoft may be looking to put together a better story of helping to keep spam off its Exchange mail servers at a time when analyst firms such as Yankee Group and Gartner have issued reports noting that managed security services are growing in popularity among enterprises.

Just last week, infrastructure provider VeriSign announced the $40 million acquisition of network security firm iDefense in an effort to expand its managed security services.

Today's announcement likely signals the software giant's growing commitment to message security and management and will play a key role in Microsoft's strategy to help customers be more secure and better protect their messaging infrastructure, according to Redmond.

"We see FrontBridge's services as a perfect complement to Exchange. The FrontBridge team brings significant expertise in helping customers mitigate messaging risks before they ever reach the corporate firewall," Thompson's statement said.

Andrew Lochart, senior director of marketing for Postini, another managed e-mail service provider, told internetnews.com that it had no plans to change its strategy, even if Microsoft will now own its direct competitor, FrontBridge.

"Certainly, enough people in the market are skeptical about getting their security solutions from Microsoft," he said. "For Microsoft to get into the security space with the purchase of a managed service provider, it will be interesting and remains to be seen what it will do with that."